Automatic pool cover systems utilizing interconnected rigid buoyant slats, which roll up on a submerged or elevated drum as described by U.S. Pat. No. 3,613,126, to R. Granderath, are popular in Europe. These pool cover systems utilize passive forces arising from buoyancy or gravity for propelling, the cover to extend the cover across a pool. With either buoyancy or gravity, there must be some mechanism to prevent a retracted cover from unwinding responsive to the passive force. Such passive force systems also have a disadvantage in that the passive force must be overcome during retraction. Granderath suggests a worm gear drive mechanism for winding the cover and preventing cover drum rotation when not powered. The slats for these are further described in U.S. Pat. No. 4,577,352, to Gautheron.
U.S. Pat. No. 4,411,031 to Stolar describes a system similar to Granderath where instead of rigid hinged buoyant slats, various floating sheet materials such as a polyethylene polybubble, or a laminate of vinyl sheeting and foamed substrate, are floated on the surface of the water. The propulsion of the cover across the pool is reliant on buoyant and gravitational forces much like the system in the Granderath patent.
Pool covers which employ floating slats or similar materials, and which use buoyant forces to propel the cover across the pool, necessarily wind the cover onto a roller drum which is positioned above or below the water surface. In the case of covers wound onto a spool sitting above the edge of the pool, such as at one end or another, when the cover is fully wound onto the cover drum, the entire rolled up cover sits above the surface of the edge of the pool. In some cases, the cover and drum are located in a separate bench apparatus setting next to the pool. The design is to aesthetically hide the cover and roller drum and also allow the entire mechanism to be manually rolled backwards away from the end of the swimming pool.
Using a separated gear drive system with limit switches to travel such a limited distance is costly and it complicates timing of the two drive systems. Furthermore, these electric drives require the supply of electrical current right next to the swimming pool which poses the possibility of a shock safety hazard. Moreover, having the electrical apparatus near the pool accelerates corrosion of the electrical components, rendering them unreliable, as well as exposing the components to flooding and costly repair.
In many known European application of such hinged lid recess systems, the manual or automatic hinged lid is shortened or made somewhat narrower, so as to partially close the recess and leave a gap or aperture sufficient to allow the slatted cover to pass through. Typically the leading edge portion of the cover is not fully retracted beneath the lid, but left remaining partly above it, so as to permit the cover to lead properly through the aperture on the covering mode of travel, i.e., during putting on the pool cover. This is important because if the leading edge of the cover was not fed properly through the aperture and jammed there, the cover drive system, which would continue to unwind, would cause the cover slats to jam and damage underneath the lid.
Typical lid systems for underwater cover drum enclosures, which incorporate an aperture or opening for cover slates to pass through, are unattractive and also create a potential safety hazard. If a swimmer steps into the aperture and is trapped, injury and even drowning can result. Consequently, most American Health and Safety inspectors do not allow such aperture design in public and commercial pools, or even some residential pools.
Another problem with slatted cover systems, which emerge from beneath the pool floor or the pool side wall or generally below the water surface, is the difficulty maintaining correct slat orientation. The cover slats move vertically upward by buoyancy at the beginning of the cycle, break the water surface, and subsequently change direction to travel in a floating horizontal direction. Often difficulties arise in assuming and maintaining correct orientation. This is often solved by having the leading slat component section pre-bent or fixed in an orientation towards the desired direction of travel. Often this is not sufficient when the cover drum is one foot or more below the water surface and the cover will often sway back and forth below the water, making direction of travel upon breaking the surface of the water unpredictable. Another possible solution is to slow down the speed of emergence of the slatted cover during the unwinding cycle to gain sufficient control until the slats break the water surface, but results are still unpredictable absent a tracking or guide system to guide the leading edge of the cover in the desired direction.
German Patent DE 3032277 A1 to R. Granderath describes a pool floor lid covering system in which an air bladder induction system is introduced to open the lid prior to allowing the cover to unwind from the cover windup roller, and to close when the cover is fully retracted. German Patent DE 198 07576 A1 to Frey describes yet another mechanism to cover the pool cover roller mechanism located in the floor of the swimming pool wherein a floating door is moved vertically to the water surface by cables that are wound up on reels from the pool cover cavity in the floor. The system utilizes a worm gear reducer drive, similar to that used to drive the pool cover drum, to actuate the door closing system. This system is generally well known. Typically, the covering hinged lid system is actuated by means of a separate worm gear reducer drive powered by an electric motor and connected to the hinged lid shaft. Electric-mechanical limit switches devices are used to stop the rotary drives which subsequently engage and power the floating lid reels and the hinged lids, at the proper point of rotation.
Hinged lids would normally only have to rotate 40 to 60 degrees to create a sufficient aperture for the slatted cover to pass through on its way from beneath the pool floor to the water surface. Using a separated gear drive system with limit switches to travel such a limited distance is costly and it complicates timing of the two drive systems. Furthermore, these electric drives require the supply of electrical current right next to the swimming pool which poses the possibility of a shock safety hazard. Moreover, having the electrical apparatus near the pool accelerates corrosion of the electrical components, rendering them unreliable, as well as exposing the components to flooding and costly repair.
Another problem with powered floor lid systems is a safety hazard inherent in other types of automatic closing doors. The lid or closure device can potentially crush a swimmers limb that is inadvertently caught between the pool edge and the lid during the closing cycle of the lid or the closing device. For this reason, it is heretofore undesirable to utilize automatic doors or lids on underwater pool cover drum enclosures.
A problem with shaft operated in-floor or in-wall lid systems is that the speed at which the lid is operated can substantially increase structural requirements of the lid system. This is a particularly important consideration at the high torque starting point of the opening cycle when the lid is raised, i.e., rotated about a hinge from a horizontal to the vertical open position.
Another problem is that lid systems which require openings or apertures for allowing the lid to be delivered from the pool floor or an underwater bench design, need only be a gap of 6–12 inches wide, i.e., an opening rotation of the lid of approximately only between about 40–60 degrees. To service the system, however, full access below the lid is required. An opening of at least 24 inches, or enough to allow a person possibly in divers gear, to pass through safely, would be required. The lid may even have to be hinged in a way to rotate a full 90 degrees or more.
Although it would be possible to incorporate current sensing devices or other means to stop the cover when encountering resistence, it is very difficult to set an accurate and workable set point since the torque applied to the lid actuator shaft varies greatly as it passes from a maximum at the horizontal position, through to zero torque at the 90 degree or vertical lid position.
Known manual or automatic lid systems provided by European manufacturers are typically made of lightweight plastic construction, and have a single, unitary integral design. Such lids are typically unattractive and it is difficult to adhere plaster or tile to these plastic components to give the lid the same look or design as the rest of the pool. Furthermore, these lid systems usually employ a single heavy stainless steel shaft running the full width of the pool which has to be of sufficient diameter to be able to transmit torque yet prevent radial deflection of the shaft at the attachment of the furthermost portion of the lid away from the actuator, in order to prevent drooping of the lid.
A problem with shaft operated on-floor or in-wall lid systems is that the speed at which the lid is operated can substantially impact and add to structural requirements of the lid system. This is particularly so at the high torque starting point of the opening cycle when the lid is raised or rotated about the hinge from a horizontal to the vertical open position.
As described in several other applications and patents by the inventor, automatic cover drive systems have to be mounted next to the swimming pool and frequently below the pool deck surface. With the exception of hydraulic drive systems as described in the inventor's prior U.S. patent and applications, most floating and slatted cover systems use electric drive systems. This creates a potential shock hazard near the pool surface area and furthermore, when these systems are even briefly submerged, or flooded, expensive damage and repair costs are often required.
The inventor's previous U.S. Pat. No. 5,184,357 entitled AUTOMATIC SWIMMING POOL COVER WITH A DUAL HYDRAULIC DRIVE SYSTEM, and inventor's U.S. Pat. No. 5,546,751 entitled ANTI-CAVITATION MANIFOLD FOR DRIVE COUPLED, DUAL MOTOR, REVERSIBLE HYDRAULIC DRIVE SYSTEMS, are both incorporated herein in their entireties.